465 traces disappear after few minutes


On The Air Transponder
 

I have a 465 that I have already done some maintenance on and that I thought was fine. Instead, when it came to using it for real, I realized that the two tracks suddenly disappear after about 3 minutes of operation. The only thing I can then see by pressing the "Find Beam" is a fixed point on the screen. Of course this is something that breaks down as it heats up ... what could it be? An electrolytic capacitor? I had already changed the critical ones ... thanks for the help, F.


Tom Lee
 

Get out your voltmeter and make some measurements of the supply rails. Takes a lot of the guesswork out of the process. You'll be able to narrow down the problem in short order.

Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/17/2022 23:36, On The Air Transponder wrote:
I have a 465 that I have already done some maintenance on and that I thought was fine. Instead, when it came to using it for real, I realized that the two tracks suddenly disappear after about 3 minutes of operation. The only thing I can then see by pressing the "Find Beam" is a fixed point on the screen. Of course this is something that breaks down as it heats up ... what could it be? An electrolytic capacitor? I had already changed the critical ones ... thanks for the help, F.




Jean-Paul
 

check HV and CRT circuit

common symptoms of bad HV transformers or voltage multiplier

j


Bert Haskins
 

On 5/17/2022 11:36 PM, On The Air Transponder wrote:
I have a 465 that I have already done some maintenance on and that I thought was fine. Instead, when it came to using it for real, I realized that the two tracks suddenly disappear after about 3 minutes of operation. The only thing I can then see by pressing the "Find Beam" is a fixed point on the screen. Of course this is something that breaks down as it heats up ... what could it be? An electrolytic capacitor? I had already changed the critical ones ... thanks for the help, F.
I had this happen to me in my 465B.

It was an opamp in the power supply, a very easy fix.

 Bert









Michael W. Lynch
 

On Wed, May 18, 2022 at 06:43 AM, Jean-Paul wrote:


check HV and CRT circuit

common symptoms of bad HV transformers or voltage multiplier

j
I would suggest that since pressing the beam finder continues to show a spot after the "trace disappears" that the HV section is probably good. The HV XFMR or HV Multiplier on these scopes typically do not "come and go", once they fail, they quit working altogether. It is possible that there is a failed component in the HV/CRT circuit. First of all, check the LV power supplies for excess ripple and correct voltage levels. LV power supplies on these scopes are always troublesome and cause these sorts of problems. After that, consider a failed component in the Sweep Generator or Horizontal Amp Circuit.

--
Michael Lynch
Dardanelle, AR


Shailendra Krishan
 

I have a 465B, which had same symptom. Trace would disappear after 2 or 3 minutes after switching on. I didn't recall whether beam finder showed something in that condition or not. In my case, it was the 47uF tantalum at the output of +15 volt supply, which was failing, and it was pulling the supply into foldback. I replaced this tantalum capacitor with a good quality electrolytic capacitor of 100uF and scope has worked since then. I discovered the problem by using power supply troubleshooting charts in the manual, and it was quite easy. Later I discovered that the tantalum was getting hot, and was discoloured as well. So visual inspection may have helped too.

Shailendra


On The Air Transponder
 

OK, me too think will be some problems in the PS section. I will update you upon this for those have similar problems, thank you.